Power management is utilized in many devices and systems to reduce power consumption and extend operation. Among the power management processes that may be utilized are link processes, in which certain links, such as links operating under a particular bus or other interconnect standard, are placed in lower power states when usage is reduced
For example, the Universal Serial Bus (USB) is one of the most common interconnects on a computing platform. The USB is a polled bus, and in operation the host controller initiates all transactions on the bus, and controls the scheduling of each transaction. The bus is an I/O (input/output) interconnect for the computer platform and may include one or more links, where a link is a communication channel between ports. USB links may be subject to power management operations, placing the links in lower power states when idle.
USB has existed under evolving standards, with USB 2.0 (Universal Serial Bus Specification, Revision 2.0, released Apr. 27, 2000) being a current standard that operates at 480 mbps (megabits per second), with development being in progress to define future versions of USB at higher speeds, such as operating at up to 5 Gbps (gigabits per second). The USB 2.0 standard defines a mechanism for suspending and resuming a link, which allows for power reduction. Further, an engineering change notice (ECN) was released for USB to address link power management. (Link Power Management Addendum ECN, released Jul. 16, 2007).